Red stone roofing

I have made a small Roofing (14` x 8.5`) with Red stones duly supported by T Irons (over the walls) at appropriate distances. Cementing on the joints of Red stone pieces has also been done on the top.

Now what further is to be done on roof top. The mason is suggesting putting 2`` layer of mud, followed by plastic sheet, again layer of mud, than putting thin brick tiles (8``x 2``) and cementing the tiles like floor to make it water proof  structure. Is it okay ?

If there any other alternatives, the same may kindly be informed .

SCK